Transport of an elongated flexible web along a desired travel path is accomplished, for example, by supporting the web at various locations with rollers or support shoes. With an ideal web, perfectly straight support shoes or rollers, and accurate support mounting and alignment with respect to the web and to each other, the web will track in the direction about the desired travel path about the supports without lateral deviation. However, in practice, such ideal conditions rarely, if ever, exist. As such as the web is transported in the desired travel path, the web additionally tends to track laterally relative to the intended path.
In certain electrographic reproduction apparatus, dielectric members are utilized in the form of elongated flexible webs transported along a desired travel path about a series of support shoes and rollers. An edge guide assembly is provided to control lateral deviation of the dielectric member web with respect to the support shoes and rollers as the web is transported in the desired travel path. Due to the fragile nature of the web, problems occur when the force of a side guide member of the edge guide assembly, acting on the edge of a transported web, exceeds the beam strength of the web. That is to say, internal or external forces act on the web to generate movement in the plane of a web in the direction lateral to movement of the web along the desired travel path. The web propagates in that direction until it meets a resistance, such as that established by a side guide member of the edge guide assembly. Since the edge guide assembly is basically fixed in location, a resultant counter force is established on the web in the plane of the web. If this force increases beyond the end-loaded beam strength of the web, the web will buckle or otherwise become undesirably distorted. Ultimately, the web may curl on itself or tear, resulting in a tracking failure and/or a hard reproduction apparatus shutdown in order to provide for service or replacement of the web.
Web-tracking systems in high volume, web based, electrographic reproduction apparatus typically utilize non-constraining roller tracking systems, such as a number of castered and/or gimbaled roller mechanisms and an edge guide assembly. The castered and gimbaled roller mechanisms react to changes in web-tracking due to variability of external loads, and minimize the relative forces exerted on the web by the side guide members of the edge guide assemblies. External loads may include receiver member feed or registration mechanisms, cleaning brushes and blades, or roller chargers. Further, external loads may vary due to variations in physical characteristics from one web to another. Web-tracking may be effected over time due to changes in the external loads, or due to differences between replacement webs. The relative force induced in the web by the edge guide assembly on the web edge is very difficult to measure. Moreover, such force is not maintained within a particular predetermined tolerance range, premature damage to the web may result.